http://galileo.phys.virginia.edu/classes/252/general_relativity.html Michael Fowler, University of Virginia: "What happens if we shine the pulse of light vertically down inside a freely falling elevator, from a laser in the center of the ceiling to a point in the center of the floor? Let us suppose the flash of light leaves the ceiling at the instant the elevator is released into free fall. If the elevator has height h, it takes time h/c to reach the floor. This means the floor is moving downwards at speed gh/c when the light hits. Question: Will an observer on the floor of the elevator see the light as Doppler shifted? The answer has to be no, because inside the elevator, by the Equivalence Principle, conditions are identical to those in an inertial frame with no fields present. There is nothing to change the frequency of the light. This implies, however, that to an outside observer, stationary in the earth's gravitational field, the frequency of the light will change. This is because he will agree with the elevator observer on what was the initial frequency f of the light as it left the laser in the ceiling (the elevator was at rest relative to the earth at that moment) so if the elevator operator maintains the light had the same frequency f as it hit the elevator floor, which is moving at gh/c relative to the earth at that instant, the earth observer will say the light has frequency f(1+v/c) = f(1+gh/c^2), using the Doppler formula for very low speeds."

The earth observer will say the frequency is f'=f(1+gh/c^2) (confirmed by the Pound-Rebka experiment), the speed of the light is c' and the wavelength is L'=c'/f'. Crucial questions:

c' = ?

L' = ?

Newton's emission theory of light:

c' = c(1+gh/c^2)

L' = c'/f' = c/f = L, where L is the initial wavelength

Einstein's general relativity:

c' = c(1+2gh/c^2)

L' = c'/f' > L

The increase in wavelength (L'>L) implied by general relativity is obviously absurd, which means that the Pound-Rebka experiment has actually confirmed Newton and refuted Einstein.

References showing that, according to Einstein's general relativity, in a gravitational field the speed of light varies in conformity with the equation c'=c(1+2gh/c^2):

http://arxiv.org/ftp/arxiv/papers/1111/1111.6986.pdf J.D. Franson, Physics Department, University of Maryland: "According to general relativity, the speed of light c as measured in a global reference frame is given by c=c0(1+2phi/c0^2), where c0 is the speed of light as measured in a local freely-falling reference frame."

http://arxiv.org/pdf/gr-qc/9909014v1.pdf Steve Carlip: "It is well known that the deflection of light is twice that predicted by Newtonian theory; in this sense, at least, light falls with twice the acceleration of ordinary "slow" matter."

http://www.speed-light.info/speed_of_light_variable.htm "Einstein wrote this paper in 1911 in German. (...) ...you will find in section 3 of that paper Einstein's derivation of the variable speed of light in a gravitational potential, eqn (3). The result is: c'=c0(1+phi/c^2) where phi is the gravitational potential relative to the point where the speed of light co is measured. (...) You can find a more sophisticated derivation later by Einstein (1955) from the full theory of general relativity in the weak field approximation. (...) Namely the 1955 approximation shows a variation in km/sec twice as much as first predicted in 1911."

http://www.ita.uni-heidelberg.de/research/bartelmann/Publications/Proceedings/JeruLect.pdf LECTURES ON GRAVITATIONAL LENSING, RAMESH NARAYAN AND MATTHIAS BARTELMANN, p. 3: " The effect of spacetime curvature on the light paths can then be expressed in terms of an effective index of refraction n, which is given by (e.g. Schneider et al. 1992): n = 1-(2/c^2)phi = 1+(2/c^2)|phi| Note that the Newtonian potential is negative if it is defined such that it approaches zero at infinity. As in normal geometrical optics, a refractive index n>1 implies that light travels slower than in free vacuum. Thus, the effective speed of a ray of light in a gravitational field is: v = c/n ~ c-(2/c)|phi| "

http://www.mathpages.com/rr/s6-01/6-01.htm "Specifically, Einstein wrote in 1911 that the speed of light at a place with the gravitational potential phi would be c(1+phi/c^2), where c is the nominal speed of light in the absence of gravity. In geometrical units we define c=1, so Einstein's 1911 formula can be written simply as c'=1+phi. However, this formula for the speed of light (not to mention this whole approach to gravity) turned out to be incorrect, as Einstein realized during the years leading up to 1915 and the completion of the general theory. (...) ...we have c_r =1+2phi, which corresponds to Einstein's 1911 equation, except that we have a factor of 2 instead of 1 on the potential term."